1. Field of the Invention
The invention relates to elongated, powered surgical instruments for use in endoscopic tissue resection. More particularly, the invention relates to an instrument having an elongated inner tube rotatably situated within an elongated stationary outer tube, both inner and outer tubes having cutting apertures at their distal ends which cooperate to resect or otherwise affect tissue during endoscopic surgical procedures.
2. Description of the Prior Art
The use of elongated surgical cutting or resection instruments has become well accepted in performing closed surgery such as arthroscopic or, more generally, endoscopic surgery. In closed surgery, access to the surgical site is gained via one or more portals, and instruments used in the surgical procedure must be elongated to permit the distal ends of the instruments to reach the surgical site. Surgical cutting instruments for use in closed surgery--also known as "shavers"--conventionally have a straight, elongated outer tubular member terminating at a distal end having an opening in the end or side wall (or both) to form a cutting port or window and a straight, elongated inner tubular member concentrically disposed in the outer tubular member and having a distal end disposed adjacent the opening in the distal end of the outer tubular member. The distal end of the inner tubular member also has a window opening having a surface or edge for engaging tissue via the opening in the outer tubular member and in many cases (but not all) cooperates with the outer opening to shear, cut or trim tissue. In some cases, such as burrs, the opening in the outer tube merely allows access to the tissue and does not otherwise cooperate with the inner window. The inner tubular member is rotatably driven about its axis from its proximal end, normally via a handpiece having a small electric motor which is controlled by finger actuated switches on the handpiece, a foot switch or switches on a console supplying power to the handpiece. The distal end of the inner tubular member can have various configurations depending upon the surgical procedure to be performed, and the opening in the distal end of the outer tubular member has a configuration to cooperate with the particular configuration of the distal end of the inner tubular member. The various configurations and combinations of inner and outer members produce assemblies, the individual and combined components of which are referred to generically as shaver blades or cutting blades. Resected tissue is aspirated through the hollow lumen of the inner tubular member to be collected via a vacuum tube communicating with the handpiece.
The aforementioned elongated surgical cutting instruments have also been produced in angled configurations in which the distal tips of the inner and outer members are aligned and offset or bent at either a fixed or variable angle from the proximal ends of the aligned inner and outer members. Examples of fixed and variable angle rotary surgical instruments are shown in U.S. Pat. Nos. 4,646,738 (Trott) and 5,411,514 (Fucci et al.), both assigned to the assignee hereof, and incorporated by reference herein. In other respects the operation of fixed and variable angle shavers is largely the same as that of the straight shavers described above.
Shaver blades are usually optimized for a particular surgical procedure or part thereof. Thus, during a procedure a surgeon may use shaver blades optimized for cutting soft tissue. If during the procedure it is necessary to resect harder tissue such as bone, the surgeon may either try to use the blade already in use or may switch to a shaver in the form of a burr or more aggressive blade. Usually the latter approach is chosen since the soft tissue blade will clog or lock-up when resecting bone. Cutting edges at the distal end of the inner tube cutting window do not have the low included angle geometry required for efficient bone resection. The high forces encountered when resecting bone tend to cause blade failure through deformation due to high torsional loads.
It would, therefore, be desirable and it is an object of this invention to produce a universal shaver blade more suitable for all types of tissue than prior art devices.
Additionally, it has been difficult to produce a practical design suitable for both side and end cutting while maintaining blade sharpness and strength. Consequently, prior art shaver blades are most often configured to produce one or the other, but usually not both. Side cutting shavers have side and end facing windows in the cylindrical wall of the outer member and the cutting edge on the inner member is designed to affect resection along the outer window rim which is on a line generally parallel or slightly inclined to the shaver axis. The term "side cutting" includes full radius resection instruments in which the plane of the outer window is angled relative to the axis. While the side facing cutters have windows which are partially end facing, they are not efficient as end cutters because the cutting edges at the distal ends of the inner and outer tube cutting windows both have large included angles. That is, the edge is not sharp enough so that resection at the distal end of the cutting window is accomplished essentially by a "pinching" action between the relatively flat inner tube edge and outer tube cutting edges passing by each other. Similarly, cutting instruments designed for end cutting are relatively inefficient as side cutters because the cutting edges at the sides of the inner and outer tube cutting windows both have large included angles. Tissue is resected in this region by the same "pinching" mechanism referred to previously. In certain cases resection efficiency has been somewhat improved by decreasing the wall thickness of the inner tube (thus making the flat edge narrower), the outer tube or both, either throughout the tube length or at the distal end radius only. Such tubes are, however, prone to deformation due to high torsional loads when the inner and outer cutting edges encounter tissues which are difficult to resect. Such deformation often results in lock-up of the shaver or metallic debris at the work site due to interference between inner tube and outer tube cutting edges.
A common goal of shaver blade production is sharpness. However, while this goal may be achieved in a variety of ways, to be truly practical the design of the blade and its method of manufacture must be adaptable to efficiently produce large volumes of shaver blades with sharp edges.
A known design (FIGS. 1-4) for improving blade efficiency is a shaver blade assembly having an outer window lying in a plane inclined to the blade axis (FIG. 1) and a dual-window inner member having inwardly facing cutting teeth (FIG. 2). The planar form of the outer window produces a teardrop window shape having a low included angle around the window periphery, although this angle is not uniform around the periphery. The dual-window form of the inner may be created by, for example, a wire EDM (electrical discharge machining) process in which the wire is passed transversely to the axis through diametrically opposed portions of the cylindrical wall of the inner member. The intersection of the cylindrical outer surface and the inwardly facing wall surface thus created defines the cutting edge. It will be understood that passing the wire through the opposed walls while keeping the wire at large radial distances from the tube axis can produce the scalloped pattern of parallel cutting edges shown in FIG. 2. As seen in FIG. 4, diametrically opposed windows are formed by shaping diametrically opposed sides of the inner member. The radially outermost edges of the periphery of the windows thus formed in the surface of the inner tube intersect with the cylindrical surface of the tube to form the longitudinally extending inner cutting edges with teeth. These edges have an included angle which decreases as the distance between the edge and the tube axis increases. The sharper this edge, the easier it is to cut tissue as these inner cutting edges rotate past the outer window periphery.
While the shaver blade described above is effective, the inner window formation limits the efficiency of the tissue resection at the distal tip and does little to enable the blade to resect hard tissue such as bone. The wall thickness at the distal tip of the outer enables the inner cutting edge to cut only tissue which can extend past this thickness and into the outer window. Because of the need or desire for a bearing contact between the distal tips of the inner and outer members (on the axis along the inner surface) and because of the rounded tip of the inner, this design is limited in its ability to do end cutting. For example, as shown in FIGS. 3 and 4, the distal tip of the prior art dual-window inner member is cut flat and is spaced from the axis. Moreover, the manufacture of a tip such as this is possibly more difficult than one would desire in a production environment.
It is accordingly an object of this invention to produce a rotating shaver blade capable of use as a side cutter and/or end cutter.
It is also an object of this invention to produce a rotating shaver blade in which the inner member has a dual cutting window configuration.
It is an additional object of this invention to produce a rotating shaver blade utilizing an inwardly facing portion of the cylindrical wall of an elongated tube to provide a cutting edge.
It is also an object of this invention to produce a rotating shaver blade capable of resecting soft tissue or hard tissue such as bone.
It is another object of this invention to produce an inner member for a shaver blade assembly, the inner member having a plurality of cutting edges at its distal tip and the cutting edges having low included angles.
It is also an object of this invention to produce such a shaver blade suitable for fixed and bendable shavers.
It is also an object of this invention to produce such a shaver blade which has a minimized tendency to seize or produce debris due to deformation of the inner or outer tube during use.
It is a further object of this invention to produce a shaver blade having a cutting edge which is resilient enough to flex in a stress-relieving manner when exposed to excessive resecting forces, thus minimizing any tendency to seize.